It is known that such air intake arrangements are in widespread use in the field of aeronautics, particularly, although not exclusively, for the purposes of renewing the air in a confined zone containing temperature-sensitive equipment and/or hazardous surroundings, of the flammable or explosive type, which require the zone to be continuously ventilated in order to avoid any risk of equipment malfunction or surrounding incident.
This is the case in particular with numerous mechanical and/or electrical devices provided in the confined annular zone between the nacelle and the outer fan case and compressor casing of an aircraft turbojet engine. These devices, such as the fades (full authority digital engine control), the accessory relay box (gearbox), the engine oil reservoir, the fluidic components, etc. for example, which are generally fixed all around the external casing and thus lie in the confined zone, are ventilated with external air that enters the arrangement through the air intake orifice to flow along the channel formed in the nacelle and be disseminated, on leaving the channel, in the confined zone. The devices, and also any oil or other vapor emanating from this zone, are ventilated with external fresh air disseminated by the air channel, contributing toward ensuring correct operation thereof.
In order to meet current legislation that requires that the appropriate confined zone have an appropriate amount of air renewed per unit time, the air passage channel of the arrangement has a preset cross section that allows enough air to flow through the channel that, on leaving it, the confined zone containing the devices that require ventilation has its air renewed.
However, because the amount of external air entering the air channel of preset cross section is dependent in particular on parameters associated with the speed of the aircraft and the altitude thereof, it is difficult for the devices that need to be cooled and the vapor that needs to be expelled to be ventilated optimally.
The problem is that although the external air entering the channel of preset cross section of the arrangement via the air intake orifice upstream and leaving downstream of this channel is sufficient in quantity to ventilate the devices correctly when the aircraft is rolling along the ground, in a take-off phase or on standby, and therefore at low speed, when the aircraft is in cruising flight at maximum speed and maximum altitude, the flow rate of air leaving the channel of the arrangement toward the zone that needs to be ventilated is, on the other hand, far too great. Measurements have revealed that, in this phase of flight, the air circulating in the confined zone through the channel of the arrangement was renewed twice as often as was required. Furthermore, the air entering the confined zone gives rise to drag which results in a loss of aircraft speed and therefore in an increase in fuel consumption of said engine.
In order to remedy these disadvantages, documents WO 2006/067296 and WO 2006/057299 describe air intake arrangements comprising shut-off means with a controllable mobile element, which means are associated with said air passage channel, and means of controlling said mobile element which are actuated, either deliberately by the pilot of said aircraft or, advantageously, automatically. In the latter instance, said control means comprise a variable-volume reservoir —cylinder/piston assembly, bladder, bellows, etc.,—which receives the total pressure exerted on said aircraft by the fluid through which said aircraft is moving and which is connected to said controllable mobile element. However, because the pressure is not stable locally this system cannot be optimal. In addition, these control means are cumbersome relative to their environment and have a tendency to give rise to vibrational or imbalance phenomena that require the whole to be reinforced, thus placing a considerable burden on said air intake arrangement. Now, in order to limit aircraft fuel consumption, aircraft designers are attempting to create more lightweight systems.